One of my favorite things about iOS 9 is picture in picture mode, which keeps a small window of a movie visible on screen at all times. Unfortunately, OS X El Capitan doesn’t have an equivalent: you can watch a movie while multitasking, sure, but it doesn’t stay on top of your window stack no matter what, which is the genius of iOS 9’s interpretation.
I’m hoping OS X 10.12 will address this issue. In the meantime, though, there’s an app that will give OS X iOS 9-style picture in picture mode. And it’s free!